JP2004253886A - Interface converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interface conversion apparatus to reduce a packet loss due to packet collision in an asynchronous channel through which packet communication is carried out. <P>SOLUTION: The interface conversion apparatus for interconnecting a synchronous channel to the asynchronous channel through packet communication transmits at least one dummy packet and packets to be retransmitted, or transmits a plurality of the same packets to be retransmitted when receiving a NAK packet due to a packet loss and re-transmitting packets. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention enables data communication between a communication line having a specific interface and a line having an interface different from this specific interface by performing data format conversion in a system for transmitting and receiving data via a network. To an interface conversion device.
[0002]
[Prior art]
In a system for transmitting and receiving data between lines having different physical interfaces, an interface converter for converting a data format according to the physical interface is interposed between the lines.
[0003]
FIG. 1 shows a general network configuration in which a digital synchronous network and a digital interface device are interconnected via an interface converter and an asynchronous line for performing packet communication.
[0004]
In FIG. 1, reference numeral 10 denotes a digital synchronous network, 11 denotes a first interface converter connected to the digital synchronous network 10 via a synchronous line 12, and 13 denotes a first interface converter via an asynchronous line 14 for performing packet communication. The second interface converter 15 connected to the device 11 and the digital interface device 15 connected to the second interface converter 13 via the synchronous line 16 are shown.
[0005]
Data received from the synchronous line 10 is temporarily stored in a data buffer of the first interface conversion device 11. The first interface converter 11 reads data of a fixed length from the buffer and generates a packet. Thereafter, a header such as a destination address is added, and the packet is transmitted to the asynchronous line 14 such as a packet line. Conversely, in the packet received from the asynchronous line 14, only the data portion is accumulated in the data buffer in the first interface converter 11 or 13, and is continuously read out and sent to the synchronous line 12 or 16. It is transmitted (for example, Patent Document 1, Patent Document 2, and Non-Patent Document 1).
[0006]
This type of interface converter generally operates in a subordinate synchronization mode in which a clock is supplied from an upper digital synchronous network (backbone network side). That is, as shown in FIG. 1, the first interface converter 11 receives a clock supply from the digital synchronous network 10 side. On the other hand, a clock cannot be supplied from the network side on the opposite synchronous line side connected thereto via the asynchronous line 14. For this reason, a configuration is adopted in which a clock is built in the second interface converter 13 and a clock is supplied from the second interface converter 13 to the digital interface device 15 to be connected.
[0007]
[Patent Document 1]
JP-A-10-032609 [Patent Document 2]
JP-A-9-261295 [Non-Patent Document 1]
"Research on Pregiochronous Network Connection Device", Research on International Communications, No. 114, Oct. 1982
[0008]
[Problems to be solved by the invention]
However, since the clock accuracy of the interface converter is generally inferior to the clock accuracy of the network, the data transmission / reception timings of the interface converters facing each other may be in a state of coincidence or a state of being shifted. The state will change periodically.
[0009]
When a wireless LAN (local area network) line is used as a part of the asynchronous line, as shown in FIG. 2A, the transmission timing is shifted between the opposed first and second interface converters. Then, the packet collision in the wireless section is small. Conversely, as shown in FIG. 2B, when the transmission timings match, the wireless LAN device attempts to transmit packets to the wireless section at the same time, and a packet collision occurs and the packet is lost. The likelihood increases. In such a case, packet retransmission is performed by error control between opposing wireless LAN devices, but there is a problem that the possibility of successive packet collisions increases when transmission timings match.
[0010]
As described above, if the state in which the packet transmission timings match between the opposing first and second interface converters and the state in which the packet transmission timings deviate periodically change, packet collisions in the wireless LAN line will occur if the states match. However, the conventional interface conversion device has a problem that there is no means for detecting and preventing them.
[0011]
Therefore, an object of the present invention is to provide an interface conversion device that can reduce packet loss due to packet collision in an asynchronous line that performs packet communication.
[0012]
[Means for Solving the Problems]
According to the present invention, there is provided an interface conversion device for interconnecting a synchronous line and an asynchronous line for performing packet communication, wherein when receiving a NAK packet due to packet loss and performing packet retransmission, at least one dummy packet An interface conversion device for transmitting a packet to be retransmitted or transmitting a plurality of identical packets to be retransmitted is provided.
[0013]
Since at least one dummy packet and a packet to be retransmitted are transmitted or a plurality of identical packets to be retransmitted are transmitted when performing packet retransmission, packet collision is reduced and packet loss is reduced. The line quality can be improved.
[0014]
When NAK packets are received continuously for a predetermined number of times, it is determined that a packet collision has occurred due to coincidence of the transmission timing between the interface conversion devices facing each other, and the packet retransmission is performed by changing the packet transmission timing. Is preferred. Changing the packet transmission timing increases the possibility of avoiding packet collision.
[0015]
It is more preferable to change the packet transmission timing up to a certain number of times. If packet loss occurs even after changing the packet transmission timing a fixed number of times, it is preferable to abandon the transmission of the packet.
[0016]
It is also preferable to change the packet transmission timing until a NAK packet due to packet loss is no longer received. As described above, when there is no change in the packet loss status even after the change in the transmission timing, the transmission timing may be changed until there is no packet loss.
[0017]
It is preferable that the asynchronous line for performing packet communication includes a wireless LAN line.
[0018]
Note that error control is usually performed between wireless LAN devices in order to improve line quality. If error control between the interface converters of the present invention is used in addition to the retransmission control on the wireless LAN line, the line quality can be further improved. Will be done. If a large delay occurs in the digital synchronous line, the line quality is degraded. Therefore, it is desirable that error control be performed only on the interface conversion device side and not performed on the wireless LAN device.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 3 is a block diagram schematically showing a network configuration according to an embodiment of the present invention.
[0020]
In the figure, 30 is a digital synchronous network, 31 is a first interface converter connected to the digital synchronous network 30 via a digital synchronous line 32, and 33 is an asynchronous line (packet line) 34 for performing packet communication. A second interface converter 35 connected to the first interface converter 31 and a digital interface device 35 connected to the second interface converter 33 via a digital synchronous line 36 are shown.
[0021]
The packet line 34 has a wireless LAN line provided with wireless LAN devices 37 and 38. If a hub is provided in the packet line, a network configuration in which a wireless LAN line and a wired LAN line (Ethernet (registered trademark) line) are mixed can be realized. Each of the first and second interface converters 31 and 33 has a digital synchronization interface and an Ethernet interface.
[0022]
Data from the digital synchronous line is input to the reception buffer of the interface conversion device, and upon completion of reception of a predetermined frame set in advance, a header or the like is added and transmitted to the Ethernet line. On the receiving side, the data portion of the packet received from the Ethernet line is taken out and input to the buffer, and is continuously read out and transmitted at the clock speed of the digital synchronous line.
[0023]
In the wireless LAN section, packet transmission is performed by a CSMA (Carrier Sense Multiple Access) function. In CSMA, a communication channel is monitored (carrier sense) before transmitting a packet, and when no other wireless station is transmitting a packet, the own station transmits. If the other station is transmitting a packet, the packet is transmitted according to a procedure of waiting for a certain period of time and attempting transmission again. As described above, packets cannot be transmitted simultaneously between the opposite wireless LAN devices, and communication is performed alternately (half-duplex communication).
[0024]
The digital synchronous line is a full-duplex line, and the Ethernet line is full-duplex or half-duplex. In the network configuration of the present embodiment, a part of the packet line is a half-duplex wireless LAN line. Therefore, in order to adopt this network configuration, the transmission speed of the wireless LAN line needs to be twice or more the transmission speed of the digital synchronous line. (Specific physical transmission rates are assumed to be 1.544 Mbit / s for the digital synchronous line and 10 Mbit / s for the wireless LAN line.)
Next, a data transmission procedure between the interface conversion apparatuses according to the present embodiment will be described.
[0025]
FIG. 4 is a diagram illustrating a data transmission procedure between the interface conversion devices when a packet is normally transmitted.
[0026]
The interface converter on the packet transmitting side continuously receives data from the digital synchronous line, and upon receiving a predetermined number of frames, converts the data into a packet with a header such as a sequence number added thereto, and transmits the packet to the Ethernet line (for example, , DATA (1)). At the time of packet transmission, the sequence number (for example, sequence number 1) of the transmitted packet is registered in the ACK waiting table, and an ACK reply from the receiving side is waited.
[0027]
The interface conversion device on the packet receiving side manages the sequence number to be received next. If the sequence number (for example, sequence number 1) of the received packet matches the sequence number to be received, an ACK is returned to the transmitting side (for example, ACK (1)). The received packet is input to a queue for transmission to the digital synchronous line, and is continuously transmitted at the line speed of the digital synchronous line.
[0028]
Upon receiving the transmitted ACK of the sequence number (for example, ACK (1)), the packet transmitting side deletes the corresponding number from the ACK waiting table and ends the data transmission.
[0029]
It should be noted that a configuration in which data transmission is performed even when ACK has not arrived from the receiving side to improve transmission efficiency is also conceivable. In the example of FIG. 4, a procedure for continuously transmitting sequence numbers 2 and 3 (DATA (2), DATA (3)) is shown.
[0030]
Although only a one-way data transmission procedure has been described in the above description, since the digital synchronous line is a full-duplex line, each interface converter requires both transmission to the Ethernet line and reception from the Ethernet line. It is carried out.
[0031]
FIG. 5 is a diagram illustrating a data transmission procedure between interface conversion devices according to the related art when a packet loss occurs.
[0032]
Although the interface conversion device on the packet receiving side manages the sequence number to be received next, in the case of FIG. 5, the packet with the sequence number 2 (DATA (1)) precedes the packet with the sequence number 1 (DATA (1)). 2)) has been received. Therefore, a NAK packet (NAK (1)) requesting the transmitting side to retransmit the packet of sequence number 1 is transmitted.
[0033]
Since the transmitting side has received NAK (1), which is the retransmission request of sequence number 1, it retransmits the packet of sequence number 1 (DATA (1)), and then receives ACK (1) for the retransmitted packet from the receiving side. Thus, transmission of the sequence numbers 1 and 2 is completed. Thereafter, the packet of the sequence number 3 (DATA (3)) is transmitted.
[0034]
As described above, in the prior art, when a packet is lost, that is, when the sequence numbers do not become continuous, error control is performed by returning a NAK, and only the lost packet is retransmitted to suppress an increase in useless traffic. ing. When the cause of packet loss is deterioration of the quality of the wireless LAN line, there is a high possibility that data can be transmitted correctly by such packet retransmission. However, if the wireless LAN device starts packet transmission at the same time and packet loss occurs due to packet collision, retransmission at the same timing may cause packet collision again.
[0035]
For this reason, in the present embodiment, a different transmission method is performed at the time of packet retransmission by NAK. FIG. 6 is a diagram illustrating a data transmission procedure between the interface conversion devices according to the present embodiment when a packet loss occurs.
[0036]
When the packet transmitting side receives the NAK packet (NAK (1)) transmitted due to the discrepancy in the sequence number at the packet receiving side, the packet transmitting side transmits the dummy packet and the packet (DATA (1)) requested by the NAK packet. resend. At this time, it is desirable to minimize the size of the dummy packet (short packet) and to minimize the transmission time.
[0037]
Even if the transmission timings of both interface converters match, and the dummy packet is lost, the subsequently transmitted retransmission data packet may collide due to the back-off time of the wireless LAN device. It is possible to reduce the possibility of packet loss and reduce packet loss, thereby improving the line quality.
[0038]
The number of dummy packets to be transmitted may be one or plural. However, when retransmitting a plurality of dummy packets, the bandwidth is used more.
[0039]
FIG. 7 is a diagram illustrating the back-off time of the wireless LAN device.
[0040]
As shown in the figure, when the first and second wireless LAN devices transmit packets at the same timing and a packet collision occurs, the wireless LAN device waits for a back-off time determined randomly by each device. And try sending the packet again. In the example of FIG. 7, since the back-off time of the second wireless LAN device is short, the packet is transmitted first. The first wireless LAN device attempts to transmit a packet after expiring the back-off time, but waits at that time because the second wireless LAN device is transmitting a packet. After the second wireless LAN device completes packet transmission, the first wireless LAN device performs packet transmission.
[0041]
FIG. 8 is a diagram illustrating a procedure for changing the transmission timing according to the present embodiment.
[0042]
Even if the packet retransmission procedure shown in FIG. 6 is performed, NAK packets may continuously occur. In this case, the packet loss is reduced by changing the transmission timing at the interface conversion device that is opposed.
[0043]
Specifically, when NAK packet reception due to packet loss has continued for a predetermined number of times (for example, three times) set in advance, the packet transmission timing is changed. The time to be changed may be a specified multiple of the clock time of the digital synchronous line or a time corresponding to the minimum packet size of the Ethernet line, and is set in advance. Even after the change of the transmission timing, the transmission timing is changed every time the NAK packet is received a predetermined number of times.
[0044]
Changing the packet transmission timing is performed up to a predetermined number of times (for example, five times). If a packet loss occurs even if the packet transmission timing is changed in this way a fixed number of times, the transmission of the packet is abandoned.
[0045]
In a modification of the present embodiment, the change of the packet transmission timing is performed until no NAK packet is received due to packet loss. As described above, when there is no change in the packet loss status even after the change in the transmission timing, the transmission timing may be changed until there is no packet loss.
[0046]
FIG. 9 is a flowchart showing a control procedure of the interface conversion device for actually implementing the above-described transmission procedure of the present embodiment.
[0047]
The interface conversion device on the packet receiving side is in a state of waiting for packet reception (step S1), and upon receiving a packet, determines whether or not this is a data packet (step S2).
[0048]
If it is a data packet, it is determined whether this is a data packet with a new sequence number (step S3). If the data packet has a new sequence number, an ACK packet is sent to the interface conversion device on the packet transmission side (step S4). If the data packet is not a data packet with a new sequence number, this data packet is discarded (step S5), and the interface converter on the packet transmitting side shifts to transmission of the next data packet (step S6).
[0049]
If it is not a data packet, it is determined whether or not this is a NAK packet for the transmitted data packet (step S7). If it is not a NAK packet, it is determined whether this is an ACK packet for the data packet in the ACK waiting table (step S8). If the packet is the ACK packet, the sequence number of the packet is deleted from the ACK waiting table (step S9), and the process proceeds to transmission of the next data packet (step S6). If it is not an ACK packet, the packet is discarded (step S10), and the process proceeds to transmission of the next data packet (step S6).
[0050]
If it is determined in step S7 that the packet is a NAK packet, it is determined whether the NAK packet has been continuously received a predetermined number of times (for example, three times) (step S11). If NAK packets have not been received a predetermined number of times consecutively, the interface conversion device on the packet transmitting side first transmits a dummy packet (short packet) (step S12), and then transmits a data packet to be retransmitted. (Step S13). The number of dummy packets to be transmitted may be one or plural. Next, returning to step S2, the interface conversion device on the packet receiving side performs an operation of determining whether the received packet is a data packet.
[0051]
If it is determined in step S11 that the NAK packet has been received a predetermined number of times in a row, it is determined whether the transmission timing change is less than a predetermined number of times (for example, five times) set in advance (step S14). If the change of the transmission timing is less than the certain number, the transmission timing is changed (step S15). If the number is equal to or more than the predetermined number, the transmission of the data packet is abandoned (step S16), and the process proceeds to the transmission of the next data packet (step S6).
[0052]
Note that the timing of changing the packet transmission timing is not limited to a fixed number as described above, and may be changed until no NAK packet is received due to packet loss.
[0053]
FIG. 10 is a diagram illustrating a data transmission procedure between interface conversion devices according to another embodiment of the present invention when a packet loss occurs.
[0054]
When the packet transmitting side receives the NAK packet (NAK (1)) transmitted due to the discrepancy of the sequence number on the packet receiving side, the packet (DATA (1)) requested by the NAK packet is transmitted a plurality of times (for example, (2 times) Retransmit continuously.
[0055]
If the transmission timings of both interface converters match, and even if one retransmitted data packet is lost, the retransmitted data packet that is subsequently transmitted will not exceed the back-off time of the wireless LAN device. Therefore, the possibility of collision is reduced, and packet loss can be reduced, so that the line quality can be improved. In the procedure of the dummy packet + retransmission data packet in the above-described embodiment of FIG. 3, if the retransmission packet is lost, retransmission is necessary again. However, according to the procedure of the present embodiment, one of the data packets is lost. However, it is possible to reliably deliver the data packet. However, when the size of the retransmission data packet is large, when retransmitting three or more data packets, a large amount of bandwidth is used.
[0056]
FIG. 11 is a flowchart showing a control procedure of the interface conversion device for actually executing the transmission procedure of the present embodiment.
[0057]
The flowchart of FIG. 11 differs from the flowchart of FIG. 9 only in that a data packet to be retransmitted is transmitted instead of a dummy packet in step S12 ′, and the other processes are the same.
[0058]
The embodiments described above are merely examples of the present invention and are not intended to limit the present invention, and the present invention can be embodied in other various modifications and alterations. Therefore, the scope of the present invention should be defined only by the appended claims and their equivalents.
[0059]
【The invention's effect】
As described in detail above, according to the present invention, at the time of performing packet retransmission, at least one dummy packet and a packet to be retransmitted are transmitted, or a plurality of identical packets to be retransmitted are transmitted. Since the number of packet collisions is reduced and packet loss is reduced, the line quality can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a general network configuration in which a digital synchronous network and a digital interface device are interconnected via an interface converter and an asynchronous line for performing packet communication.
FIG. 2 is a diagram for explaining packet loss in the general configuration of FIG. 1;
FIG. 3 is a block diagram schematically showing a network configuration according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a data transmission procedure between interface converters when a packet is transmitted normally.
FIG. 5 is a diagram illustrating a data transmission procedure between interface converters according to the related art when a packet loss occurs.
6 is a diagram illustrating a data transmission procedure between the interface conversion devices according to the embodiment of FIG. 3 when a packet loss occurs.
FIG. 7 is a diagram illustrating a back-off time of a wireless LAN device.
FIG. 8 is a diagram illustrating a procedure for changing a transmission timing according to the embodiment of FIG. 3;
FIG. 9 is a flowchart showing a control procedure of the interface conversion device for actually executing the transmission procedure of the embodiment of FIG. 3;
FIG. 10 is a diagram illustrating a data transmission procedure between interface conversion devices according to another embodiment of the present invention when a packet loss occurs.
FIG. 11 is a flowchart showing a control procedure of the interface conversion device for actually executing the transmission procedure of the embodiment of FIG. 10;
[Explanation of symbols]
10, 30 Digital synchronous network 11, 31 First interface converter 12, 16, 32, 36 Synchronous line 13, 33 Second interface converter 14, 34 Asynchronous line 15, 35 Digital interface device 37, 38 Wireless LAN device

Claims (6)

An interface conversion device for interconnecting a synchronous line and an asynchronous line for performing packet communication, comprising: when receiving a NAK packet due to packet loss and performing packet retransmission, at least one dummy packet and a packet to be retransmitted; An interface conversion device for transmitting a plurality of identical packets to be transmitted or retransmitted. 2. The interface conversion device according to claim 1, wherein when the NAK packet is received continuously for a predetermined number of times, the packet retransmission is performed by changing a packet transmission timing. 3. The interface conversion device according to claim 2, wherein changing the packet transmission timing is performed up to a certain number of times. 4. The interface conversion device according to claim 3, wherein if packet loss occurs even after changing the packet transmission timing a predetermined number of times, transmission of the packet is abandoned. 3. The interface conversion device according to claim 2, wherein changing the packet transmission timing is performed until no NAK packet is received due to packet loss. The interface conversion device according to claim 1, wherein the asynchronous line that performs the packet communication includes a wireless LAN line.

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